linux-kernel - Re: [PATCH 3/3] lp8788-charger: fix wrong ADC conversion

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Message-ID: <507FE604.8070404@metafoo.de>
Date:	Thu, 18 Oct 2012 13:20:36 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	"Kim, Milo" <Milo.Kim@...com>
CC:	"cbou@...l.ru" <cbou@...l.ru>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Jonathan Cameron <jic23@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] lp8788-charger: fix wrong ADC conversion

Hi,

On 10/18/2012 08:11 AM, Kim, Milo wrote:
>  To get the battery voltage and temperature, IIO ADC functions are used.
>  LP8788 ADC driver provides RAW and SCALE channel information.
>  Both RAW with SCALE values are used for the ADC calculation.
>  The scale is micro unit, additional conversions are required in each case.
>  This patch fixes wrong ADC result.
> 
> Signed-off-by: Milo(Woogyom) Kim <milo.kim@...com>
> ---
>  drivers/power/lp8788-charger.c |   18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/power/lp8788-charger.c b/drivers/power/lp8788-charger.c
> index 02fc9ab..3c739e6 100644
> --- a/drivers/power/lp8788-charger.c
> +++ b/drivers/power/lp8788-charger.c
> @@ -239,19 +239,26 @@ static int lp8788_get_vbatt_adc(struct lp8788_charger *pchg,
>  				unsigned int *result)
>  {
>  	struct iio_channel *channel = pchg->chan[LP8788_VBATT];
> +	int raw;
>  	int scaleint;
>  	int scalepart;
>  	int ret;
> +	unsigned long tmp;
>  
>  	if (!channel)
>  		return -EINVAL;
>  
> +	ret = iio_read_channel_raw(channel, &raw);
> +	if (ret != IIO_VAL_INT)
> +		return -EINVAL;
> +
>  	ret = iio_read_channel_scale(channel, &scaleint, &scalepart);
>  	if (ret != IIO_VAL_INT_PLUS_MICRO)
>  		return -EINVAL;
>  
>  	/* unit: mV */
> -	*result = (scaleint + scalepart * 1000000) / 1000;
> +	tmp = raw * scaleint + div_u64(raw * scalepart, 1000000L);
> +	*result = (unsigned int)tmp;


We now have a function in the IIO core which does the sampling + conversion
in one step: iio_read_channel_processed. This basically allows you to reduce
this function to

	return iio_read_channel_processed(channel, result);

I'd also make the result parameter of lp8788_get_vbatt_adc signed, since
both power_supply_propval.intval and iio_read_channel_processed use a signed
int.

>  
>  	return 0;
>  }
> @@ -304,19 +311,26 @@ static int lp8788_get_battery_temperature(struct lp8788_charger *pchg,
>  				union power_supply_propval *val)
>  {
>  	struct iio_channel *channel = pchg->chan[LP8788_BATT_TEMP];
> +	int raw;
>  	int scaleint;
>  	int scalepart;
>  	int ret;
> +	unsigned long tmp;
>  
>  	if (!channel)
>  		return -EINVAL;
>  
> +	ret = iio_read_channel_raw(channel, &raw);
> +	if (ret != IIO_VAL_INT)
> +		return -EINVAL;
> +
>  	ret = iio_read_channel_scale(channel, &scaleint, &scalepart);
>  	if (ret != IIO_VAL_INT_PLUS_MICRO)
>  		return -EINVAL;
>  
>  	/* unit: 0.1 'C */
> -	val->intval = (scaleint + scalepart * 1000000) / 100;
> +	tmp = raw * scaleint + div_u64(raw * scalepart, 1000000L);
> +	val->intval = (unsigned int)tmp * 10;
>  

Same here

>  	return 0;
>  }

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